Horizontal directional drilling (HDD) is a widely accepted construction alternative to open-cut trenching. The use of HDD is preferred in many construction applications because it can emplace utility lines and conduits, such as power lines, gas lines, telephone lines, and fiber optic cables, without disturbing surface structures (roads and sidewalks), existing landscaping, trees, and shrubs; or when open-cut trenching is impractical or impossible because of existing surface structures or other obstacles such as rivers, streams, lakes, and ponds. HDD emplaces these utility structures by forming a borehole under the surface of the earth without open-cut trenching.
HDD activities are intrinsically transient or itinerant. The HDD machine typically is brought to the jobsite by truck or trailer, along with all necessary drilling components, tools, and adjuncts (drill string or pipes, water tanks, water, drilling mud, conduits, and the like). The HDD machine is taken from the truck or trailer and placed on the ground in a proper orientation with respect to the intended drill path. A small pit, called the entrance pit, typically is dug slightly ahead of the HDD machine to allow the drill string and drill bit to enter the ground at the correct orientation. The HDD machine then advances the drill string through the ground as it is navigated by various means known to those skilled in the art. The HDD machine typically continues to advance the drill string and drill bit until the drill hit reaches the desired location. Typically, a small pit (called the exit pit or target pit) is dug as the far terminus of the bore path.
The product line (typically a power line, gas line, telephone line, fiber optic cable, or other underground utility) is then installed in the borehole by any of several different techniques. If the product line is small and of a suitable construction, it may be attached to the end of the drill bit—or to a special fitting which replaces the drill bit—and simply may be pulled through the newly-created bore hole as sections of drill string are removed from the machine end of the drill string. In other cases, a small-diameter conduit (for example, PVC plastic conduit) may be attached to the end of the drill bit and pulled through the newly created bore hole as drill rod is removed from the machine end of the drill string. Once the conduit is emplaced, product lines may be either pulled or blown through the newly emplaced conduit. If the product lines are large in diameter, as might be the case for water lines, the drill bit is replaced by a larger-diameter backreamer which is, in turn, connected to the product line or a conduit. The backreamer enlarges the borehole as the backreamer and product line or conduit are pulled back through the borehole while drill rod is removed from the machine end of the drill string. After the product is installed, connections are made at the entrance and exit pits and the pits are then filled with earth, at which time the HDD machine with its related apparatus is placed back on the truck or trailer for removal to the next job site or to a storage facility in anticipation of the next job.
A typical contemporary HDD machine consists of a number of specialized mechanisms and mechanical devices. For example, the prime mover (or primary source of operating power) is an internal combustion engine. The internal combustion engine is almost always a diesel engine, although smaller units may occasionally employ gasoline engines. The internal combustion engine then drives mechanisms and devices which generate thrust and pullback forces (advancing or retracting the drill string) and rotational forces (rotating the drill string in the desired direction). The internal combustion engine also operates other equipment, such as a hydraulic pump, providing operating power to various machine mechanisms such as pipe grippers (vise jaws which grip the drill pipe while making or breaking connections between individual drill rod segments), hydraulic motors providing operating power to install anchoring augers, positioning mechanisms to raise and lower the machine frame, and rod handlers to reduce the amount of manual effort required to add or store drill rod before or after use. Machine operation is often done using hydraulic valves and hydraulic cylinders; although some HDD machines have machine controllers which are electrically powered and which, in some cases, provide varying degrees of machine automation.
An alternative embodiment of the drill string described above is a two-pipe system with each section of drill string comprising an outer and an inner drill string that are independently rotatable. Dual-member drill strings are comprised of a plurality of pipe joints, each of which comprises an inner member supported inside an outer pipe or member. The inner member of the drill pipe constantly drives rotation of the boring head and drill bit to excavate the formation, and the outer member of the drill string is selectively rotated to align a steering mechanism to change the direction of the borehole while the rotating bit continues to drill. An exemplary HDD system is disclosed in U.S. Pat. No. 5,682,956, the content of which is incorporated herein in its entirety.
Internal combustion engines are the mainstay of portable construction equipment, and they have a great many desirable features for industrial applications. These features include portability, maturity of the technology, generally acceptable reliability, and the use of readily available fuel.
The present invention teaches the use of electrically powered underground construction and ancillary equipment to avoid any potential drawbacks associated with internal combustion engines. The objective of the present invention is to provide operating power by means of fuel cells. The advantages of this invention are set forth in the following paragraphs.